Naturally occurring phytosterols have generated strong interest in the functional food industry as the plant sterols have been proven to lower the levels of serum low-density lipoprotein (LDL), the so-called bad cholesterol in humans. Phytosterols are plant compounds with chemical structures similar to that of cholesterol. This structural and functional similarity of phytosterols can actually block food-based cholesterol from being absorbed into the bloodstream. The result is that both phytosterols and dietary cholesterol end up excreted in waste matter.
Tall-oil-pitch (TOP) is an undistilled residue from the distillation of crude tall oil (CTO), which is a dark brown mixture of fatty acids, rosin, and neutrals including phytosterols, liberated by the acidulation of soap skimmings from the alkali (sulfate) process, derived from wood pulping processes, which are primarily used in making paper. Typical TOP is known to have about 15% free and bound sterols, about 40% free and bound fatty and rosin acids, about 10% bound wax alcohols (C16-30 alcohols), about 25% heavy molecules, and about 10% other compounds of terpenoids, steroids, and unknowns. A major component of the neutral fraction, concentrated in the TOP of the CTO, is a class of compounds known as phytosterols, including β-sitosterol as the major sterol component.
There has been a great deal of interest and effort in recovering the phytosterols and their derivatives of fatty acids and other biologically significant molecules, which are particularly useful as dietary supplements and as food additives, in order to reduce cholesterol levels in humans, thus reducing the risk of heart disease, according to current clinical studies.
Therefore, the interest and value of recovering phytosterols from TOP sources has increased, and the resolution of all of the problems associated with recovering phytosterol from TOP have become of great interest. It is most desirable that a viable commercial process achieves a high percent recovery of sterols (greater than 70% recovery is preferable), while desirably achieving sterol purity of at least 98%.
During recovery of high purity phytosterols, a class of natural molecules of fatty alcohols also known as wax alcohols and policosanol, present in TOP, was found to co-crystallize with phytosterols. Policosanol is a natural mixture of fatty alcohols ubiquitous in plant waxes. The TOP feed that we processed contains common aliphatic alcohols in which three significant policosanols are present, namely, 1-dodecosanol, 1-tetracosanol, and 1-hexacosanol.
As described hereinafter, the invention addresses this problem and achieves the desired yield and purity of phytosterols from TOP prevailing over fatty alcohols and other undesirable impurities, and describes making corresponding phytosterol esters using different acylating reagents.
U.S. Pat. No. 6,465,665 discloses a process of obtaining, inter alia, sterols from TOP in which the process achieves sterol purities of 95-96%. See Examples 3 and 4. This patent describes a continuous process for the recovery of sterols from mixtures of neutral matter obtained from crude tall oil (CTO) black liquor soap skimmings or tall oil pitch, comprising the steps of a series of distillations using a rectifying column, condenser and thin film reboiler so as to form a first to fourth fractions comprising long chain aliphatic alcohols, sterols concentrate and esters, sterols concentrate, and sterol esters depending on the distillation stages. Then the third fraction was recrystallized from a mixture of a hydrocarbon solvent, short chain aliphatic alcohol, and water. The residue from the mother liquor was recycled as the mixture of neutral matter of very first feed.
EP 1250350B1 describes a composite crystalline structure comprising a phytosterol or a derivative thereof and a phytostanol or a derivative thereof prepared by dissolving a phytosterol or esterified derivative thereof purified from its source and a phytostanol or esterified derivative thereof purified from its source in a solvent at an ambient temperature or temperature above ambient but lower than the boiling point of the solvent, cooling the solvent to allow crystal formation; and filtering and washing the crystals so formed; wherein the structure has a single composite endotherm as determined using differential scanning calorimetry.
It remains desirable to provide a process that achieves even higher purity levels of sterols recovered from TOP. As discussed hereinafter, the process of the present invention provides such desirable higher purity levels of sterols.